2 weeks feels a bit pressured to me for content with a lot of achievements. 4 weeks feels better for those.
They've been dialing this in as they go, if they keep up with 1 patch being 1 month long and the 2nd patch having permanent content in it along with rolling any dungeons back into Fractals (or any combination like that), I'll be pretty happy. Btw, did you catch Colin's comment about Invasions being permanent? Just imagining where they can go with this....
https://forum-en.guildwars2.com/foru...o-Decide/first